In automatic clutch systems, the disengagement travel at the clutch disk is determined; the friction torque at the clutch being controlled using this disengagement travel. In this context, the clutch is operated by an electromechanical actuator, which is controlled by a control unit, and whose forces are hydraulically transmitted to the clutch. To directly determine the travel at the disengaging clutch disk, a displacement sensor system is situated at the clutch disk, if possible.
In addition, indirect methods for determining the travel at the disengaging clutch disk are known, in which absolute and/or incremental displacement pickups are placed in the mechanical part of the electromechanical actuator. In this context, in one specific embodiment, the zero position of the mechanical part of the electromechanical actuator is fixed by a mechanical limit stop. By actuating the electromechanical actuator against the limit stop and measuring the applied actuation energy, the zero position is electronically detected and taken as a basis for the further measurements.
Under ideal conditions, in which incompressibility of the fluid and a rigid system are assumed, and where the system also does not have any leaks, the distance which the mechanical part of the electromechanical actuator travels is proportional to the distance which the disengagement system travels. However, in real clutch systems, disturbances due to air, temperature, elasticities and leaks occur, so that the position of the clutch measured by the sensor system does not correspond to the actual position of the clutch.
The disturbances triggered by air, temperature and elasticities are normally compensated for by adaptations. Disturbances due to leakage may not be permanently compensated for and must therefore be detected, in order to identify a defective system.